Precious metals recovery from waste materials using an induction furnace

ABSTRACT

A method of recycling electronic waste and recovering valuable metal components from electronic waste which involves feeding electronic wastes such as cell phones, computers, pagers, personal data assistants, handheld global positioning devices, MP3 players, calculators, batteries, etc. into an induction furnace that is changed with a mass of liquid iron. A portion of organic components of the electronic waste can be removed prior to feeding the electronic waste into the induction furnace and/or volatilized or decomposed in the induction furnace. The metal components of the electronic waste form separate liquid layers in the induction furnace that are separated according to their densities. The separated metals layers are recovered either in a solid or liquid phase.

TECHNICAL FIELD

The present invention relates to methods for recycling small electronic items such as cell phones, pagers, personal data assistants (PDA's), etc. More particularly, the present invention is directed to apparatus and methods for recovering valuable metals from small electronic items.

BACKGROUND ART

Electronic items such as computers, cell phones, pagers, personal data assistants (PDA's), handheld global positioning systems (GPS's), MP3 players, calculators, batteries, etc. are quickly becoming a significant source of electronic waste. As technology advances, consumers are replacing such electronic items with newer models and newer equipment more and more frequently. Due to a very small after-market demand for used electronic equipment, the quantity of these materials that is being thrown away in landfills has been increasing at an alarming rate. One current estimate is that there are over 100 million used cell phones in the United States alone with at least one manufacturer replacing 250,000 cell phones monthly.

The discarding of electronic equipment creates a two-fold problem. First, the electronic equipment often contains hazardous materials such as lead, cadmium, mercury, etc. that can be of concern when discarded in an improper fashion. The second problem is that the electronic equipment may also contain valuable metals such as gold, silver, etc. that are lost.

Small electronic items such as cell phones, pagers, personal data assistants (PDA's), etc. contain, in addition to plastics and other organic materials, a small amount of copper, lead, tin, gold, iron, aluminum, zinc, cadmium, etc. The more abundant valuable materials, including gold and silver would be worth recovering if there existed an efficient and economic process to perform such recovery.

One of the basic problems encountered when developing processes for the recovery of materials from the electronics industry has been the high cost associated with the dismantling of equipment. This is especially true for smaller handheld items such as cell phones, pagers, personal data assistants (PDA's), handheld global positioning systems (GPS's), MP3 players, calculators, and other personal computing devices. The small nature of these devices makes it difficult to provide good separation of the various components into useful materials for recycle.

There has been a great deal of discussion concerning the best manner to handle the recycle and reuse of electronic equipment. There are a number of programs that have been established for the collection of these items. Current programs include the dismantling of equipment into steel, copper, aluminum, plastic, circuit boards and power supplies. This can be a very time consuming and labor intensive process. The recovery of precious metals from the dismantled equipment is usually handled by sending material to smelters for processing.

The present invention provides for an apparatus and process for recycling small electronic items and for recovering valuable metals there from. Moreover, the invention provides an alternative for the recovery of valuable metals that are present in materials separated in dismantling operations and in some cases can replace the dismantling operation, or allow more automated methods to be used for material separation.

DISCLOSURE OF THE INVENTION

According to various features, characteristics and embodiments of the present invention which will become apparent as the description thereof proceeds, the present invention provides a method of recovering metals from electronic wastes which comprises:

-   -   providing an induction furnace;     -   maintaining a charge of iron in the induction furnace;     -   feeding electronic wastes into the induction furnace;     -   allowing organic components of the electronic waste fed into the         induction furnace to volatilize or be decomposed;     -   allowing volatile metal components of the electronic waste to         volatilize;     -   allowing other metal components of the electronic waste fed into         the induction furnace to melt and separate by density into         different metal layers within the induction furnace; and     -   recovering the different metal layers from the induction         furnace.

The present invention further provides a method of recycling electronic wastes including cell phones, pagers, personal data assistants, handheld global positioning devices, MP3 players, and calculators, which method comprises:

-   -   providing an induction furnace;     -   maintaining a charge of iron in the induction furnace;     -   feeding the electronic wastes into the induction furnace;     -   allowing organic components of the electronic waste fed into the         induction furnace to volatilize or be decomposed;     -   allowing volatile metal components of the electronic waste to         volatilize;     -   allowing other metal components of the electronic waste fed into         the induction furnace to melt and separate by density into         different metal layers within the induction furnace; and     -   recovering the different metal layers from the induction         furnace.

The present invention further provides a liquid bath that comprises a mass of liquid iron and the metal components of a charge of electronic waste that was added to the mass of liquid iron and melted therein.

BRIEF DESCRIPTION OF DRAWINGS

The present invention will be described with reference to the attached drawings which are given as non-limiting examples only, in which:

FIG. 1 depicts a system according to the present invention that uses an induction furnace to recover valuable metals from electronic waste according to one embodiment of the present invention.

FIG. 2 depicts a system according to the present invention that uses an induction furnace to recover valuable metals from electronic waste according to another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention involves methods and apparatus for recovering valuable components from electronic waste. According different embodiments, the present invention limits or completely avoids manual separation of the components of electronic waste.

The invention makes use of an induction furnace that maintains a bath of liquid metal into which electronic waste such as cell phones, pagers, PDA's, etc. are fed. The liquid metal bath can be iron or any other suitable metal which can be maintained a sufficient temperature to process electronic waste as described below. The temperature of the liquid bath provides sufficient energy to melt, volatilize or destroy all of the components of the electronic equipment. Metal portions of the feed materials with high boiling points such as iron, copper, tin, lead, gold, silver, etc. will melt at the process operating temperature. These metals will then either dissolve in the iron bath, or be separated in layers due to differences in specific gravity.

Lighter metals such as zinc, cadmium, mercury, etc. and organic materials would volatilize and exit the furnace as gases. These gases could be either collected or processed through an afterburner. Since induction furnaces use electric current as their energy source, gases are not produced to provide the energy for the process, this results in lower volumes of gas to be treated. The lower gas volume will allow more alternatives to be evaluated for the treatment of the gases exiting the process.

According to one embodiment, the electronic waste items are fed directly into the liquid metal bath without any preprocessing. In such a process, organics, such as plastic cases or housings, keypads, display screens, gasket/seal elements, oils, etc. will either volatilize or be decomposed (then volatilized from the system) while volatile metal components will volatilize out and other metal components will be melted into the liquid metal bath where they can be removed from the bath or form separate liquid layers that are arranged by their densities.

When the organic materials are volatilized or decomposed in the induction furnace, the resulting exhaust is subjected to appropriate containment, including scrubbing, bag house collection, treatments, etc. to prevent environmental pollution.

According to another embodiment of the present invention the electronic waste items are subject to a preprocessing step that removes a percentage of the organic components. A suitable preprocessing step would involve sorting the organic components from the metal components. This can be done according to the present invention by subjecting the electronic waste items to a process of crushing, cutting and/or grinding to reduce the electronic items into smaller pieces and using air to blow off the lighter organic components or using a water bath to float off the lighter organic components. The use of air to blow off the lighter organic components could be used in conjunction with a conveyer system, a fluidized bed, a falling stream of the ground, cut and/or crushed electronic waste, or any other conventional physical separation apparatus.

The present invention will be discussed with reference to FIGS. 1 and 2 in which common reference numerals have been used to identified similar or common elements where possible to avoid having to repeat descriptions of such similar or common elements.

FIG. 1 depicts a system according to the present invention that uses an induction furnace to recover valuable metals from electronic waste according to one embodiment of the present invention. In FIG. 1 an induction furnace 1 which can be of the coreless or channel type is schematically depicted. A liquid metal bath 2 is provided within the induction furnace which only partially fills the induction furnace 1. The bath 2 is maintained at a temperature sufficiently high to volatilize or decompose organic material components of the electronic waste and to melt metal components within the electronic waste. In the case of using iron as the liquid bath, the bath 2 is maintained at a temperature of from about 1,300° C. to about 1,600° C. The liquid metal bath 2 fills only a portion, e.g., about 25% to 50% of the furnace capacity.

In the embodiment of the invention depicted in FIG. 1, electronic waste including cell phones, pagers, PDA's etc are fed directly into induction furnace 1 through feed line 3. As the organic components volatilize or decompose from the electronic waste, the resulting gases, including particulates, are captured by exhaust system 4 and transferred to course/heavy particulate separator 5 such as a cyclone separator and then into a sock or bag filter 6. The course/heavy particulates are removed from the separator 5 through line 7 and the remaining fines or dust are removed from the sock or bag filter through line 8. Arrows 9 depict the direction of flow of the exhaust gas stream. Clean air leaves sock or bag filter 6 through line 10. If necessary a scrubber can be used to further condition the exhaust from the induction furnace 1.

Components of the electronic waste which are easily oxidized such as calcium, silicon, magnesium, aluminum, etc. will form slag that floats on the top of the metal bath 2. This slag layer can be skimmed off using conventional techniques and subjected to further processing or disposal. Metals with higher densities such as gold, silver, lead, copper, etc. will form separate layers at the bottom of the furnace. Metals such as zinc, cadmium, mercury, etc. that are volatile at the operating temperature of the system will exit the furnace as a vapor and, if desired, can be collected using conventional techniques or otherwise contained for environmental purposes.

While the bath 2 in the induction furnace 1 is being heated it is subject to turbulent conditions owing to the effect of the high intensity induced currents that are typical in induction furnaces. This turbulence helps mix the electronic waste into the bath and helps even out the temperature in the bath.

After a period of time during which electronic waste have been fed into the induction furnace 1, the induction current used to heat the charge is turned off so that the turbulent conditions of the charge are minimized. As the charge settles, various liquid metal layers will become arranged according to their specific gravities or densities. Table 1 below lists the densities for various metals that can be recovered from electronic wastes and the melting points of the metals. TABLE 1 Metal Density (g/cm³) Melting Point (° C.) Iron 7.87 1536 Nickel 8.90 1455 Copper 8.96 1083 Silver 10.53 961 Gold 19.3 1063 Lead 11.34 327

From Table 1 it can be seen that after turbulent conditions in the bath are reduced, the components will settle out by density. Several of the metals will form alloys with either the iron or copper in the metal bath. The iron with its alloys will typically float on top of the bath. The heavier alloys with the copper will form the lower layers of the bath.

It is to be understood that the separation of the various metal layers may not be complete so that all of the individual metals can be recovered in their pure form. However, the process of separation effected by the use of the liquid iron bath will allow sufficient separation of the individual metals or metal alloys which can, if necessary be subject to further purification using known techniques.

In FIG. 1, the various separated metals and metal alloys can be removed from the induction furnace 1 via line 11. According to one embodiment of the process, one or more product outlet line 11 can be provided at a variable depth in the induction furnace 1 and used to draw off a desired, separated metal layer. Such a process would allow for continuous processing of electronic waste. It is also possible to progressively remove the various separated metal layers from the top down using and repositioning the outlet of line 11, or progressively remove the various separated metal layers from the bottom using the outlet line 12 that is provided at the bottom of the induction furnace 1. It is also possibly to allow the entire bath to cool and solidify and thereafter recover the various separated metal layers in their solidified form. Otherwise, based upon differences in melting points of the various metals it is possible to remove selected ones of the separated metals by their phase differences.

The process depicted schematically in FIG. 1 does not involve pretreating or preprocessing the electronic waste.

FIG. 2 depicts a system according to the present invention that uses an induction furnace to recover valuable metals from electronic waste according to another embodiment of the present invention. According to the process depicted in FIG. 2, electronic waste to be recycled or processed to recover valuable metals is initially subjected to a process that separates a portion of the organic components (plastic, rubber, etc.) from the metal components. The separation process utilizes a physical sizing apparatus 20 such as crusher, grinder, cutter or other suitable means to break the individual electronic waste items apart and into pieces that can be mechanically separated in the next step.

Following processing in the sizing apparatus 20, the electronic waste is subjected to a process that separates at least a portion of the organic components from the metal components. Such a process utilizes a physical separation apparatus 21 that can, for example, use an air stream(s) to blow away/off the lighter organic components or use a liquid such as water to float off the lighter organic components in a bath. The use of air to blow away/off the lighter organic components could be used in conjunction with a conveyer system, a fluidized bed, a falling stream of the ground, cut and/or crushed electronic waste. It is to be understood that the overall preprocessing can be performed by any other conventional physical separation apparatus(es).

In FIG. 2 the preprocessed waste is separated into a feed stream 22 that contains the metal components and a stream 23 that contains organic components. The organic components which leave the physical separation apparatus 21 via line 23 can be recycled to recover plastic components.

Accordingly, there are fewer pollutants generated when the electronic waste enters the induction furnace 1. Of course, the exhaust from the induction furnace 1 has to be contained and subject to any necessary environmental cleaning/treatment using conventional apparatus and possible recovery of volatile metal vapors. Accordingly, a particulate separator 5 and a sock or bag filter 6 as depicted in FIG. 1 could be incorporated into FIG. 2.

As in the process depicted in discussed in reference to FIG. 1, metal components would separate in the induction furnace 1 in FIG. 2 and could thereafter be removed and collected in a similar manner.

The liquid metal bath 2 in the induction furnace 1 is intended to serve primarily as a heat reservoir to carry out the separation process described above. The bath 2 can be replaced and/or replenished if it becomes contaminated with components that adversely effect the metals that are to be separated and collected. During the operation of the process a slag layer will form on the surface of the bath 2. The slag layer can be controlled using conventional methods. For example, the thickness of the slag layer can be controlled by the addition of suitable chemical slagging agents or by mechanically removing, e.g. skimming, the slag layer off the bath 2.

The system can be operated in a continuous or batch mode. In the continuous operation, feed material, i.e. electronic waste can be continuously added to the process with slag and metals being removed at various levels from the bath 2. If the process is operated in a batch manner, feed materials would be added until the furnace was full, then the slag and a portion of the liquid metal bath would be removed before additional feed material is added.

Although the present invention has been described with reference to particular means, materials and embodiments, from the foregoing description, one skilled in the art can easily ascertain the essential characteristics of the present invention and various changes and modifications can be made to adapt the various uses and characteristics without departing from the spirit and scope of the present invention as described above and set forth in the attached claims. 

1. A method of recovering metals from electronic wastes which comprises: providing an induction furnace; maintaining a charge of iron in the induction furnace; feeding electronic wastes into the induction furnace; allowing inorganic components of the electronic waste fed into the induction furnace to volatilize or be decomposed; allowing volatile metal components of the electronic waste to volatilize; allowing other metal components of the electronic waste fed into the induction furnace to melt and separate by density into different metal layers within the induction furnace; and recovering the different metal layers from the induction furnace.
 2. A method of recovering metals from electronic wastes according to claim 1, wherein the electronic wastes consists of handheld consumer electronic devices.
 3. A method of recovering metals from electronic wastes according to claim 2, wherein the consumer electronic devices comprise at least one of a cell phone, computer, a pager, a personal data assistant, a handheld global positioning device, an MP3 player, and a calculator.
 4. A method of recovering metals from electronic wastes according to claim 1, wherein the recovered metal layers comprise at least one of gold and silver or alloys of these metals.
 5. A method of recovering metals from electronic wastes according to claim 1, wherein a portion of the organic components of the electronic waste is removed before the electronic waste is fed into the induction furnace.
 6. A method of recovering metals from electronic wastes according to claim 5, wherein the portion of the organic components of the electronic waste is removed by reducing the size of the electronic waste and removing organic components after the size reduction.
 7. A method of recovering metals from electronic wastes according to claim 6, wherein the removed organic components are subject to recycling.
 8. A method of recovering metals from electronic wastes according to claim 6, wherein the metal components of the electronic waste that are fed into the induction furnace are pre-heated.
 9. A method of recovering metals from electronic wastes according to claim 1, wherein the process is a continuous process.
 10. A method of recovering metals from electronic wastes according to claim 1, wherein the process is a batch process.
 11. A method of recovering metals from electronic wastes according to claim 1, wherein the different metals that are recovered are subject to additional purification processes.
 12. A method of recovering metals from electronic wastes according to claim 1, wherein at least one of the different metals is recovered in a liquid form.
 13. A method of recovering metals from electronic wastes according to claim 1, wherein at least one of the different metals is recovered in a solid form.
 14. A method of recycling electronic wastes including cell phones, computers, pagers, personal data assistants, handheld global positioning devices, MP3 players, and calculators, which method comprises: providing an induction furnace; maintaining a charge of iron in the induction furnace; feeding the electronic wastes into the induction furnace; allowing inorganic components of the electronic waste fed into the induction furnace to volatilize or be decomposed; allowing volatile metal components of the electronic waste to volatilize; allowing other metal components of the electronic waste fed into the induction furnace to melt and separate by density into different metal layers within the induction furnace; and recovering the different metal layers from the induction furnace.
 15. A method of recycling electronic wastes according to claim 14, wherein the recovered metal layers comprise at least one of gold, silver and platinum.
 16. A method of recycling electronic wastes according to claim 14, wherein a portion of the organic components of the electronic waste is removed before the electronic waste is fed into the induction furnace.
 17. A method of recycling electronic wastes according to claim 16, wherein the portion of the organic components of the electronic waste is removed by reducing the size of the electronic waste and removing organic components after the size reduction.
 18. A method of recycling electronic wastes according to claim 14, wherein the removed organic components are subject to recycling.
 19. A liquid bath that comprises a mass of liquid iron and the metal components of a charge of electronic waste that was added to the mass of liquid iron and melted therein.
 20. A liquid bath according to claim 19, wherein the electronic waste comprises at least one of cell phones, pagers, personal data assistants, handheld global positioning devices, MP3 players, and calculators.
 21. A liquid bath according to claim 20, wherein the liquid iron comprises about 25 to 75 percent of the volume of the total bath. 